A lot of high reactivity, reactive oxygen species such as superoxide anion radicals (O2−.), hydrogen peroxide (H2O2), hydroxyl radicals (.OH), singlet oxygen (1O2) [excited molecules], etc. are generated in a human body, particularly in mitochondrias, microsomes, leukocytes, etc. It is reported that such reactive oxygen species are involved in biological defense including ecological defense, biochemical reactions, etc. In normal cells, these reactive oxygen species are formed in about 1 mol % of a redox reaction, a main reaction, and the generated reactive oxygen species are metabolized by decomposing enzymes, etc.
Though 95% or more by mass of oxygen taken into a human body by aspiration is turned to water through a usual metabolism process, the remaining few percentages of oxygen is turned to reactive oxygen species in electron transfer systems such as mitochondrias and microsomes. In most cases, the generated reactive oxygen species are removed by antioxidant enzymes such as superoxide dismutase (SOD), glutathione peroxidase, etc.
However, all reactive oxygen species are not necessarily removed from the human body even with these antioxidant enzymes, so that part of the reactive oxygen species oxidize proteins, lipids, nucleic acids, etc. Though part of oxidized substances are repaired by a biological defense mechanism, some of them remain damaged. It is considered that the accumulation of substances damaged by oxidation in a human body causes diseases and aging.
The amounts of expressed antioxidant enzymes such as SOD, etc. decrease with age. If decrease in the ability to remove reactive oxygen species by aging and excess production of reactive oxygen species by disease overwhelm the metabolism, the reactive oxygen species are accumulated, resulting in the nonspecific oxidation of cell components such as lipids, etc. and thus the death of cells. The accumulation of reactive oxygen species causes aging, and many diseases such as habit-related diseases, Alzheimer's disease, etc.
When a human body takes a large amount of oxygen by vigorous sports or labor, he suffers from the generation of excess reactive oxygen species, and loses moisture and minerals by fatigue and perspiration, resulting in decrease in the activity of antioxidant enzymes and thus the accumulation of large amounts of active oxygen species in the body. Having sports drinks, etc. containing minerals is effective to recover from fatigue by making up for the lost moisture and minerals. However, because conventional sports drinks do not have ability to remove reactive oxygen species, they are substantially ineffective to remove reactive oxygen species from the body. Accordingly, demand is mounting for drinks capable of efficiently removing reactive oxygen species from the body, which can be easily taken while playing sports.
It is known that vitamins such as vitamin C, vitamin E, etc. have ability to remove reactive oxygen species. Drinks containing these vitamins are commercially available and easy to have. However, limited amounts of vitamins are absorbed in the digestive organs, and excess vitamins are excreted through the kidney. Even if one has large amounts of vitamin-containing drinks, vitamins cannot be kept at high concentrations in the body. Also, the vitamins themselves are oxidized by the reactive oxygen species, losing the ability to remove reactive oxygen species. The oxidized vitamins function as oxidants to oxidize proteins, lipids, nucleic acids, etc. in the body. This indicates that too high concentrations of vitamins are rather harmful to the body. It is thus said that vitamins are double-edged swords for humans. Accordingly, having a large amount of a vitamin-containing drink once to efficiently remove reactive oxygen species is likely to be harmful to the health.
JP 2002-212102 A discloses electrochemically and biologically active micro-particles providing rich anions to the body, and supplying negative charges to receptors in the body tissue while passing through the digestive organs, to keep the biological activity of the receptors. The electrochemically and biologically active micro-particles specifically described therein are colloidal platinum particles treated by a surfactant, etc. It is also described that the electrochemically and biologically active micro-particles can be added to soft drinks, etc. It is further described that the metal salt-reducing method, etc. described in JP 2001-79382 A can be used in the production of the electrochemically and biologically active micro-particles.
The metal salt-reducing method of JP 2001-79382 A comprises adding a solution of metal ions of platinum, etc. and a pH-adjusting agent (sodium hydrogen carbonate, etc.) to a treatment solution comprising a reducing agent (ethanol), a nonionic surfactant (colloid-protecting agent) and water, and heating the resultant mixed solution while stirring to reduce the metal ions to form metal colloid. According to this method, a high-concentration colloidal metal dispersion with little agglomeration of metal colloid particles can be produced by adjusting a treatment solution temperature, the proportions of the surfactant and the reducing agent to the metal ion solution, etc.
JP 2001-79382 A describes only Polysorbate 80 as a nonionic surfactant. However, it has been found that a colloidal platinum dispersion containing Polysorbate 80 as a colloid-protecting agent has insufficient ability to remove reactive oxygen species. In addition, Polysorbate 80 per se is not permitted as a food additive that can be added to drinks in Japan. Accordingly, the colloidal platinum dispersion containing Polysorbate 80 as a colloid-protecting agent is not only unsatisfactory for drinks, but also suffers from safety problems.
JP 10-68008 A discloses a method for producing a colloidal platinum dispersion by adding ethanol as a reducing agent to a chloroplatinic acid solution containing Polysorbate 80, stirring the resultant mixture while heating, and subjecting the mixture to a dialysis treatment using an ultrafilter to remove Polysorbate 80. JP 10-68008 A describes that Polysorbate 80 does not remain in the colloidal platinum dispersion obtained by this method, and that the colloidal platinum particles per se are not precipitated because of negative charge.
However, it is considered that because Polysorbate 80, a kind of the colloid-protecting agents, is combined to the colloidal platinum particles, for instance, by association, adsorption, coordination, etc., part of Polysorbate 80 remains in the colloidal platinum dispersion even after the dialysis treatment using an ultrafilter. Also, the inventors' research has revealed that the colloidal platinum particles per se are not charged, failing to keep a colloidal state without a colloid-protecting agent.
Further research has revealed that colloidal platinum particles in the colloidal platinum dispersion prepared by the method of JP 2001-79382 A have a wide particle size distribution, which largely differs from lot to lot. However, because large colloidal platinum particles are not absorbed in a human body through digestive organs, they fail to remove active oxygen species in the body. Further, because a higher percentage of large colloidal platinum particles results in decrease in the total surface area of the colloidal platinum particles at the same platinum concentration, the ability of the colloidal platinum dispersion to remove reactive oxygen species is inevitably lowered. Also, if the particle size distribution largely differed from lot to lot, the percentage of large colloidal platinum particles having substantially no contribution to the removal of reactive oxygen species would be different even at the same platinum concentration, resulting in a varying percentage of effective colloidal platinum particles and thus extreme difference in the ability to remove active oxygen species. Accordingly, the method of JP 2001-79382 A fails to produce a colloidal platinum dispersion having stably high ability to remove reactive oxygen species.
It is known to use polyvinylpyrrolidone, dodecanthiol, sodium polyacrylate, methyl cellulose, etc. as protecting agents of metal colloids. Among these protecting agents, sodium polyacrylate is a permitted food additive causing no safety problems. It has been found, however, that when ethanol is removed from the nanocolloidal platinum dispersion obtained by the method of JP 2001-79382 A using sodium polyacrylate as a protecting agent, the dispersion becomes sticky, failing to form a uniform colloidal platinum dispersion by adding water.